The present invention relates to a method of making foamed aluminum products to be used as sound-absorbing or heat-insulating materials.
Foamed aluminum is capable of absorbing sound or insulating heat, and so is used in the form of sound insulating walls for freeways as an example.
The foamed aluminum has a cell structure comprising cells of uniform shape, and is prepared by melting aluminum (Al) or alloys thereof, as shown in FIG. 2A, stirring the melt with a specific amount of calcium (Ca) added as a viscosity increaser for increasing the viscosity of the melt, re-stirring the melt with a specific amount of hydrogenated titanium (TiH.sub.2) added as a foaming agent, as shown in FIG. 2B, for foaming the melt in a closed state. For instance, see Japanese Patent Application Laid-open No. JP-B-1-51528.
Foamed metals including foamed aluminum are generally formed from a melt in a vessel, and an important point is to what degree a stable and uniform structure (density) is developed the resulting foamed structure. As is known in the prior art, a block a of foamed aluminum is formed in a conventional vessel, as shown in FIG. 2C. Then, only a region b having a relatively stable structure and desired density, located at the middle of the vessel, is cut out of the block a for use. A (hatched) region c having an insufficient degree of foaming (high density and high strength), located in the vicinity of the inner wall of the vessel, is unsuitable for sound-absorbing or heat-insulating material, and so is rejected or discarded. This makes the yield of conventional methods very low. It is also very troublesome to cut out only the middle region b suitable for sound-absorbing or heat-insulating material and to make products therefrom.
An object of the present invention is to provide a method of producing foamed aluminum products having reasonable sound-absorbing and heat-insulating properties and possessing the local strength and rigidity needed for mounting, and fastening which makes intentional use of both uniform and non-uniform structures obtained at the foaming step, thereby providing a solution to the problems encountered with conventional methods.